Tire Shake

Discussion in 'The Comp Buzz' started by Rob Harrison, Sep 4, 2011.

  1. TobyG

    TobyG New Member

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    Hell yea its 4 times better not to sound like a wise ass. One other thing, if you change rear gear ratios often, make a math channel that will show you axle rpm. Its the real way to compare tire speeds between two runs with different rear gear ratios. If you change tire roll outs often, go a step further and make a math channel to show tire speed. Its not exact because you don't know tire growth but it works pretty good.

     
  2. Terry Spargo

    Terry Spargo Member

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    One of the first things I check is 1/4 second drive shaft speed and I want to see 1700 rpm not 1000 rpm. I also have the rear pnuematic shock sweeps set on hard for the first 1.3 seconds. I nomally don't have shake problems with a controlled engine stall rpm with either of the Hemi comp bullets but stall rpm becomes more of an issue with the 800" top sportsman power and the 1300 ftlb's of torque.
    Terry A/AP :eek:
     
  3. Patrick Hale

    Patrick Hale New Member

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    Toby - before the "radar systems" a team used a spring loaded 5th wheel, mounted directly under the right side axle tube. It was in contact with the ground and had magnets to measure the RPM. Knowing the small wheel diameter you could accurately calculate ground speed.

    It was also possible to measure the "ride height" of the axle tube and in that way get the "loaded radius" of the tire at the contact patch using a linear potentiometer just like those used today on shocks. With rear axle RPM and "tire radius" you get the real "tire speed" and with the spinning 5th wheel you get "ground speed" to allow you to create a math channel to calculate "slip ratio".

    Wow - this was 25+ years ago! NHRA banned the use of the 5th wheel. :)

    Patrick Hale
    www.DragRacingPro.com
     
  4. TobyG

    TobyG New Member

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    Keep in mind Terry's DSRPM number works for his rear gear and tire size.

    Axle rpm with 1700 dsrpm is 340rpm with a 5.00 gear and 413 rpm with a 4.11.

     
  5. TobyG

    TobyG New Member

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    Sounds like a fun deal. We put one on a Pro Mod car a while ago. We weren't too sure what people would say using it so we put it on the ground using a cylinder right at the end of the burnout and lifted it back up at the finish line. It was some fun data.

     
  6. Terry Spargo

    Terry Spargo Member

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    Toby G is really sharp..no shake...don't hit the bars to hard..look at the div 6 photos of my heap and Ray Hadfords gorgeous rail..and my Cavaliers bars hardly touch the track. Its the car to the left of the pic...
    Terry A/AP
     
  7. Rob Harrison

    Rob Harrison Well-Known Member

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    Toby and Pat, that's some pretty trick stuff you have dealt with, through all the KJ shake problems, was there any one thing that would trigger shake FOR SURE, or is it a combo of things. I don't know what we would do with more data, we have been on a goose chase for awhile now, all from data that we were interpreting wrong. More data should push us over the brink, we're already booked into the nut house.
     
  8. TobyG

    TobyG New Member

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    A while ago, I came up with the wheelie bar sensor. It was a pretty interesting device. I started using it on Scelzi's FC (the E-Moola/No-Moola car) with a strain gaged bolt. It worked out great yet it was something designed for a test lab and not a race track. It was a $700 bolt and would last a couple of races. One day hanging out with my old man on his farm, I looked at a hydraulic cylinder and realized we could measure WB hit with hydraulic pressure. So I made a few and it opened alot of eyes. I am not saying I had any idea what we would 'see' but it really changed how people view what the wheelie bars do. Finally we could associate what the dsrpm is doing when the wheelie bar was on the ground and how much pressure was applied to the bars.

    It was always the assumption that when you hit the bars, you unloaded the tire. For those with the sensor on your car you already know, the harder you hit the bar, the harder you plant the tire. Now if you don't have the power required to keep the tire round when this hit occurs, it goes out of round and you are screwed.

    I have drank alot of beer and Crown thinking about the magical answer to curing tire shake. So far I have only accomplished some spirited bull shit sessions with other tuners and alot of hangovers. So I am still working on the magical cure for the tire shake and the hangover.

     
  9. Patrick Hale

    Patrick Hale New Member

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    Top Secret Graph

    Toby - take out the beer and Crown and have a long look at this graph. It shows how the tire grip is affected by the slip ratio. This is just generic data, so don't get wrapped around the actual values of force and slip.

    There are two types of tire shake. What I call "strong shake" is on the left side of the curve, at lower slip ratios (Pro Stock cars at the launch). "Weak shake" is on the right side. "Weak shake" is what you commonly see on Fuel cars in the so-called "shake zone".

    The fixes for "strong" and "weak" tire shake are the exact opposite of each other (Garlits was so smart with his list :D). The first step is to figure out where you are on the slip ratio curve and then move to the area of maximum grip.

    Patrick Hale
    www.DragRacingPro.com
     

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  10. Rob Harrison

    Rob Harrison Well-Known Member

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    So it's starting to sound like....a little shake is a good thing...in the threshold if you will, gripping and spinning. I bet it would be impossible to get a radial to shake, they have low rolling resistance, but I presume that is because they don't wrinkle, which appears to be part of this shake thing.
     
  11. steve1724

    steve1724 Member

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    Mark

    No one really knows, so they are reading this thread very carefully.:cool:
     
  12. caveman

    caveman New Member

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    I think you are correct. I know of a few comp teams that have tried to switch to radials, but the radials did not work well with the clutch cars. I think there is very small tuning window to have a controlled tire slip. In stock and super stock where they tend to dead hook off the line the radials would pick up quite a bit after the rear shocks were softened up a bit.
     
  13. Dan Bennett

    Dan Bennett Member

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    This thread is bringing back some fond (and not so fond) memories.

    In the mid 90s I was convinced that the sampling rate of the data recorders was way too slow. I caught a lot of grief from that, especially from the guys who were selling the "standard" computer. The problem was that there wasn't much of an alternative at the time. Pi existed but was at that time totally sports car based, so when I'd ask them about getting some features included that was important to drag racers I'd get either apathy, a blank stare, or both. We were one of the first to double the magnets where we could and it was considered top secret stuff at the time.

    I had realized that of all the important things we were tracking, we had no idea of the ground speed of a car. Even if we ran a curve for wheelspeed, there was no way to determine for sure how much of it was spin and how much was actually driving the car.

    I managed to find an optical sensor to measure ground speed that was being used, but couldn't get the team I was working for to step up and spend the money. It was pretty trick in that it put out a beam to the pavement and calculated how long it took to run over it - we're only talking about a few inches here. Since it depended on actually reading the surface, you'd have to use some sort of illumination if it was dark out.

    Later that next year I was at Englishtown during a night session, standing under the tower where the cars came through on their way to the water. A car fired up right next to me and I noticed there was a soft light now shining on my feet. I squatted down and saw the sensor tucked in in front of the rear wheel. As I stood up, the crew chief was looking at me with a "busted!" look on his face.

    Later I got to work with some big inch IHRA stuff and find out what tire shake REALLY was.

    I don't have the years of experience of Patrick or Toby, but I got the really strong impression that tire shake was a function of the difference in tire/engine/vehicle accelleration being too far out of phase. If any one of the three was markedly different, you were going to have problems. If the engine and wheel speed were up there, but the car's speed wasn't you're asking the tire to do something it can't possibly do.

    Others may disagree, but in my mind there are two types of shake. One is most common and comes from wheel speed that's too low. The other comes from too high wheel speed (blowing the tires off) but it's really a completely different thing. Both have to do with the structural integrity of a tire and forces that will get it out of round.

    Not that a legend like him needs my agreement, but Glidden's statement that you have to spin the tire is dead on. When you hear Pro Stock people talking about getting up on the tire, that's what they mean.

    Finally, I'm convinced that the car's accelleration must always be ahead of the tires. I wish I would make it clearer than that, but it's hard to explain.

    Thanks to all the really smart people who've posted comments here; I'm enjoying this thread a lot.
     
  14. Patrick Hale

    Patrick Hale New Member

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    Dan - Thanks for sharing you thoughts!

    I totally agree how difficult it is to type out a few words on a site like ICR to explain what we feel in our gut. We all have racked our brains on these topics and come up with a mental image of how these fickle racecars work. Sometimes the racecar throws you a bone . . . but most of the time it's a curve ball - and we have to adjust and change our theories.

    Dan - you've given me some new ideas to think about! Are you going to Phx, Vegas or Pomona later this year?

    Patrick Hale
    www.DragRacingPro.com
     
  15. Rob Harrison

    Rob Harrison Well-Known Member

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    I was standing on a starting line with Les Davenport, when he was crew chief and everything else , for Cy Chesterman. It's hard to imagine what's going on in his head, at any given time, but his car left and it black-tracked the 1st 1/2 of the track, he leaned over and said "that's gona be fast", sure enough he was low by 5 or 6.

    Somewhere in that observation, lies the window between shake and fast , the relationship is the same from Comp to alcohol and the alcohol cars don't have shocks to help deal with shake (if they do in fact help deal with it).

    What you said, Dan, offers a fairly clear image, "If the engine and wheel speed were up there, but the car's speed wasn't you're asking the tire to do something it can't possibly do" . The more this gets hashed around, tire construction is maybe the most important part, if a tire is stiffer, it is less likely to distort and shake. Now comes the Comp car tire issue, How much does it weigh? Most Comp teams wouldn't even consider a tire that was 5 lbs. heavier......
     
  16. Dan Bennett

    Dan Bennett Member

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    You've hit on why this is so rewarding yet so frustrating at the same time - there are a bunch of interconnected variables ready to bite you at every turn, but when you get it right...

    Someone previously mentioned degrees of shake. I think that's exactly it. I was always looking for the tire to "quiver" at the top of first gear and I suppose that quivering is actually very mild shake.

    Though a stable tire should always be the goal, we can go overboard. I think we absolutely need some tire distortion at the hit. It provides some suspension and some energy storage. Where we run into problems is when we go too far in any direction.

    Whether you can stand more weight in the wheels/tires depends entirely on each combination and package. It's going to be slower to accellerate which might help you on the leave but hurt you going down the track. I got out of the business before beadlocks were mandated, but in testing I could always go quicker without them - assuming I got things half way right in the first place.

    Then again, I don't ever remember anyone complaining about not being able to find a small enough circumference tire from Goodyear. We were always looking for something with more and more rollout.

    Like I said, fun but frustrating.
     
  17. Rob Harrison

    Rob Harrison Well-Known Member

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    Didn't that whole beadlock thing go back and forth, heavier by a bunch so they got to be slower, then Pro Stock went to work on them (or the set up) and they ended up being faster BECAUSE of less tire distortion?
     
  18. JustinatAce

    JustinatAce Member

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    I don't think a beadlock distorts any less or more.. The issue is that the rim cannot spin inside of it. Alcohol guys don't run them because it narrows the window...
     
  19. Patrick Hale

    Patrick Hale New Member

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    Here's another video showing a variety of tire shakes.

    http://www.youtube.com/watch?v=mfJejgODr3E&feature=related

    There are examples of both "strong shake" and "weak shake" in this video. Watch for the early "strong shake" at low wheel speed and low slip ratio. "Weak shake" occurs farther down track with high slip ratio.

    I added the TireSlip graph from my earlier post below. It shows how the tire grip is affected by the slip ratio. Again, this is just generic data, so don't get wrapped around the actual values of force and slip. The peak tire grip also varies with the track and tire temperatures.

    Rob - tire shake is usually not the fault of the tire, or caused by the tire design. It's up to the tuner to navigate the slip ratio curve - starting at 0% slip before the clutch (or transbrake button) is released, rising to the "area of maximum grip" and then sliding back toward the left side of the graph at lower slip ratios as the racecar goes down the track.

    The fixes for "strong" and "weak" tire shake are the exact opposite of each other. The first step is to figure out where you are on the slip ratio curve and then change your combination to move back toward the "area of maximum grip".

    Patrick Hale
    www.DragRacingPro.com
     

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  20. C Tanksley

    C Tanksley New Member

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    If they made tires like they did in the early 90`s we would`nt even be talking about tire shake . Goodyear screwed up the tires when they moved to Chily and they will never be the same . I look at the guys that run B/ED now compaired to tires of 94 and 95 would be at least .05 faster if they had a new set of 1288 to bolt on . The sidewall was so thin sometimes that they would leak air through the sidewall . The bead was so thick that you could put in as long a wheel screw as you wanted . The tire would grow tall and still keep lots of rubber on the ground . Great tires, wish we had them now .
     

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